Pen



FIG. 1 is a perspective view of a pen showing a new design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof; and,

FIG. 4 is a left view thereof.

The subject matter shown in dashed lines is for illustrative purposes and forms no part of the claimed design. 

CLAIM The ornamental design for a “pen,” as shown and described. 